1. Field of the Invention
The present invention relates to a resin-packaged semiconductor device.
2. Description of the Related Art
An example of prior art semiconductor device is shown in FIGS. 9A and 9B. The illustrated semiconductor device includes a semiconductor chip 9, a pair of conductors 8A, 8B made of a metal plate, and a resin package 7 for sealing them. The semiconductor chip 9 is mounted on the conductor 8A, and the conductor 8A is electrically connected to a lower electrode (not shown) of the semiconductor device 9. The semiconductor chip 9 includes an upper electrode 90 electrically connected to the conductor 8B via a wire W. The paired conductors 8A, 8B respectively include a thicker portion 81a, 81b and a thinner portion 82a, 82b. The thicker portion 81a, 81b has a lower surface exposed at the bottom surface of the resin package 7 as a terminal 83a, 83b for surface-mounting. As shown in FIG. 9B, the terminal 83a, 83b is rectangular.
With this structure, the semiconductor device can be surface-mounted on a desired portion by utilizing the terminals 83a, 83b. Since each of the conductors 8A, 8B includes an upper surface having a larger area than that of the terminal 83a, 83b, the semiconductor chip 9 and the wire W can be appropriately bonded to these portions. The thinner portions 82a, 82b of the conductors 8A, 8B are sealed in the resin package 7. Consequently, part of the resin content of the resin package 7 exists under the thinner portion 82a, 82b for fixing and supporting the conductors 8A, 8B.
However, the above-described prior art semiconductor device has the following disadvantages.
Due to a strong demand for an overall size reduction in the field of semiconductor devices, the semiconductor device needs to be reduced with respect to its length, width, and/or height. In realizing such a size reduction of the semiconductor device, it may be difficult for the conductor 8B to have an enough size as a whole because the conductor 8A must have a sufficient size for mounting the semiconductor chip. Even under such a situation, the terminal 83b must have a reasonable size for appropriate surface-mounting.
To increase the terminal 83b in size, the thicker portion 81b may have an increased dimension b, as shown in FIG. 9A. However, the dimension a of the thinner portion 82b reduces due to this structure, resulting in a reduction of the resin content of the resin package 7 existing directly under the thinner portion 82b. As a result, the resin package 7 may not provide sufficient support for the conductor 8B, which may easily cause crack formation at the corners of the resin package 7.
Further, if the width c of the thicker portion 81b is increased to increase the area of the terminal 83b, the resin package 7 will have a correspondingly reduced width d on both sides of the thicker portion 81b. Consequently, crack formation may easily occur in these areas. Particularly, in molding the resin package 7, the corners of the resin package 7 may be insufficiently filled with resin because of the reduced width d, which may easily leads to crack formation.
Thus, an attempt to reduce the overall size of the conventional semiconductor device will lead to higher likelihood of crack formation with respect to the resin package 7, consequently posing a hinderance to a size reduction of the semiconductor device. While the above description is given only with respect to easier crack formation near the conductor 8B which is reduced in size, the same problem may also apply to the relationship between the conductor 8A and the resin package 7.
It is an object of the present invention to provide a semiconductor device which, even if reduced in overall size, is unlikely to suffer crack formation with respect to a resin package, and which can be appropriately surface-mounted on a desired portion.
According to the present invention, a semiconductor device is provided which comprises a semiconductor chip, a plurality of conductors electrically connected to an electrode of the semiconductor chip, and a resin package for sealing the semiconductor chip and the conductors. Each of the conductors has a thicker portion and a thinner portion. The thicker portion includes a lower surface exposed at a bottom surface of the resin package as a terminal for surface-mounting. The thicker portion of at least one of the conductors is non-rectangular with partially or entirely uneven width.
According to the present invention, the non-rectangular thicker portion includes a relatively wide portion and a relatively narrow portion due to its partially or entirely uneven width. Due to the provision of the thicker portion and the thinner portion for the conductor, a width decrease of the thicker portion results in a corresponding size increase of the thinner portion. According to the present invention, therefore, even where the conductor cannot be made to have a sufficient overall size, the thicker portion and the terminal provided by the thicker portion for surface-mounting can retain a reasonable size for surface-mounting without unduly reducing the area of the thinner portion, as opposed to the prior art semiconductor. As a result, according to the present invention, the semiconductor device is unlikely to suffer crack formation with respect to the resin package while being capable of being appropriately surface-mounted on a desired portion, thereby contributing to an overall size reduction.
According to a preferable embodiment of the present invention, the resin package includes a pair of first side surfaces spaced in a direction x, and a pair of second side surfaces spaced in a direction y perpendicular to the direction x. The terminals of the conductors are paired with and spaced from each other in the direction x. The non-rectangular thicker portion includes a tapered portion having width increasing in the direction y toward a center of the resin package. The tapered portion may be generally trapezoidal, triangular, or semicircular.
With this structure, when the resin package is formed by utilizing a mold, the tapered portion functions as a guide for molding resin to smoothly flow into the corners of the resin package (where the first and the second side meet). Consequently, the corners of the resin package are prevented from remaining incompletely filled with resin, thereby reducing the possibility of crack formation.
Preferably, the conductor has an outer end projecting from a respective first side surface and formed with a recess. With this structure, solder flows into the recess to increase the bonding area of the solder relative to the conductor in surface-mounting the semiconductor device, which improves the mounting strength of the semiconductor device.
Preferably, the recess extends over an entire thickness of the thicker portion. This helps the solder smoothly flow into the recess.
Other features and advantages of the present invention will become clearer from the detailed description of the preferred embodiments given.